The present invention relates to an exercise measuring instrument in which exercise in walking, jogging, running, and the like is measured utilizing an acceleration sensor which uses a piezoelectric element and the like, and the measured exercise is informed.
Devices such as a pedometer are well known which are used to count the number of steps taken by the user of such devices while he or she is walking or jogging for the health. For example such devices are shown and described in U.S. Pat. Nos. 4,144,568, 4,192,000, 4,223,211 and 4,387,437.
In pedometers described in the above U.S. Pat. Specifications, a magnetic sensor or a mechanical sensor is used as a sensor detecting walking or jogging. This results in a relative complexity in the sensor-construction and thereby the devices are made not only large in size but also are easy to be damaged by an external shock and the like.
While, U.S. Pat. Nos. 4,510,704 and 4,651,446 disclose techniques where pedometers are installed in Boots or shoes in which pedometers a piezoelectric element is used. Though in both the above U.S. Patents an electronic circuit is not concretely disclosed for processing a signal supplied from the piezoelectric element, it is considered that in case an electric signal generated by vibration of the piezoelectric element is relatively small, the electric signal is amplified by an amplifier and the number of steps is calculated by counting points at which a level of the amplified electric signal varies.
By the way, the above-mentioned pedometers using the piezoelectric element are installed in Boots or shoes, but when these pedometers are worn for example on the wrist or the waist of the user of the device, the electric signal generated by the vibration of the piezoelectric element is extremely small, so that an amplifier with a high gain must be employed for accurately detecting the electric signal.
However, the piezoelectric element generates an electrical signal having a certain amplitude when the user is walking, and it also generates another electrical signal having an amplitude greatly different from that of the former signal when the user is jogging. Therefore, there is a disadvantage that if the amplifier is set to a "high gain", the electrical signal generated when the user is walking may be detected while the electric signal generated when the user is jogging cannot be detected, because of the excessively large amplitude of the electrical signal resulting from the high gain of the amplifier. On the other hand, there exists another disadvantage that if the amplifier is set to a "low gain", the electric signal may be detected which is generated when the user is jogging but the signal can not be detected which is generated when the user is walking, because the signal is too small to be detected.